| 摘要 |
The cap has a tubular base (20) receiving a pressure responsive closure (10) which is retained in a closed position. The closure has an inner transverse wall (26) which, in the closed position, defines upper (19) and lower (21) sections between which is a normally closed valve. The valve opens at a difference in pressure between the upper and lower sections. The cap has a semi-open position in which a gas vent (24) communicated with a the lower part of the base.
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